We are studying the immunological reactivity of the gastrointestinal tract in diseases in which certain immunological factors may play a role. The overall objective of these studies is to gain insight into possible pathogenic mechanisms. We have concentrated on inflammatory bowel disease (IBD) and, in particular, on the lymphocytes of the intestinal lining--lamina propria lymphocytes (LPL). These cells are located at the site of tissue pathology and may bear more relevance to the disease process than peripheral blood lymphocytes. We are studying their involvement in mitogen-induced as well as spontaneous-cell mediated cytotoxicity, possible mechanisms of tissue damage in these diseases. We also are examining the effects of corticosteroids on the function of LPL. We are developing an animal model for IBD using the guinea pig in an effort to expand our understanding of potential ways in which the immune system may initiate pathologic changes in the colon.